#include <REGX52.H>

void Delay(int xms)	//@12.000MHz
{
	unsigned char data i, j;
	for(xms;xms>0;xms--)
	{
		i = 2;
		j = 239;
		do
		{
			while (--j);
		} while (--i);		
	}
}

void main()
{
	while(1)
	{
		if(P3_1 == 0)
		{
			Delay(20);
			while(P3_1 == 0);
			Delay(20);
			P2--;	
			// 1111 1111 -> 1111 1110 -> 1111 1101 ...			
		}
	}
}